The tractor and the trailer in the coupled together condition form a road train. Road trains in the form of a semitrailer or articulated train generally have a maximum transport volume. For this, the cargo space is configured in box shape, but it must satisfy legal requirements in regard to its dimensions. The desire for maximum transport volume on the one hand and observance of legal requirements in terms of outside dimensions on the other hand complicate the design of aerodynamically favorable vehicle shapes and thus a reduced fuel consumption or emission of pollutants.
Wind deflectors are known from the prior art to lessen the aerodynamic drag, being arranged on the roof of the tractor and able to adjust their inclination by motor in order to adapt themselves to the different heights of the trailer or become as flat as possible when driving empty.
WO 20061029732A1discloses one such wind deflector on the roof of the tractor of a semitrailer, which is furthermore outfitted with a shifting mechanism for a fifth wheel. When driving slow, the fifth wheel can move to the rear on the tractor, so that a wider gap is adjusted between the front wall of the trailer and the rear wall of the driver's cabin, which is advantageous for maneuvering and traveling tight curves. To reduce the aerodynamic drag when traveling fast and in a straight line, this gap can be reduced by moving the fifth wheel in the direction of the driver's cabin, thus reducing the concomitant turbulence at the gap. The wind deflector arranged on the roof should likewise be connected to the control unit of the shifting mechanism and thus be adjustable in its inclination to the size of the gap, so that the inclination is more flat for a large gap and more steep for a narrow gap.
In practice, however, it turns out that the placement of a wind deflector located on the roof of the driver's cabin is not enough to reduce the aerodynamic drag in the desired degree.